The art of distributed processing in which data processing is shared between a central processor and a group of local processors is now being applied to digital telephone business customer systems. In such systems, information is typically exchanged between a central processor and a local processor via a conventional synchronous type data bus. A bus contention scheme administered by the central processing unit or administered locally by each distributed processor is invoked to prevent information placed on the bus by one local processor from colliding with information placed on the same bus by a second local processor. In such schemes a local processor may employ a bus management arrangement to gain access to the bus, for example recognizing its signature or address on the bus for the reception of information. Typically, a bus management arrangement is interleaved with information processing to maintain synchronization with bus timing signals.
Bus administration arraangements, while orderly, reduce the real time processing capability of a local processor. For business communication systems, a reduction in real time is adverse to the concept of distributed processor systems implemented for the purpose of enhancing real time data processing capability through distributed processing. Consequently, the number of communication port circuits managed by a local processor would have to be reduced to offset the real time loss imposed by a bus administration arrangement.
The real time processing capability of a distributed processor communication system is further degraded by programmed maintenance tasks which monitor the health of local processors. For a large communication system, the running of maintenance tasks could consume an appreciable portion of the system's real time. This problem is especially aggravated when a faulty local processor impairs common equipment, such as a system bus. Under such circumstances there may be a need to suspend data or call processing in order to invoke fault recognition tasks to identify the faulty processor and isolate it by removing it from service.
Various schemes aimed at relieving a processor of the burden of managing a bus and of providing sanity control have been proposed. However, such schemes appear to be limited to organizing bus access on a priority basis or providing a common pool of memory shared by a local processor and a central processor.
For example, the distributed multiprocessor communication system disclosed in U.S. Pat. No. 4,223,380 issued to J. C. Antonaccio et al, describes an arrangement for relieving a central processing system of the burden of interprocessor bus management. The Antonaccio bus management scheme essentially dedicates a portion of a system time frame to each system processor module in order to transmit information. Interprocessor communication is acknowledged by a receiving processor by transmitting an acknowledgement signal upon receiving information via a interprocessor bus. The Antonaccio system is limited in that it provides no provision for locally detecting and isolating a faulty processor module which is corrupting the information transmitted via the interprocessor bus. Further, the Antonaccio system is not applicable to large communication systems in which real time processing is critical since each processor module has dedicated to it a portion of each time frame for transmission whether or not it has information to transmit. While this is advantageous for guaranteeing that each processor module will have equal access to the system bus it is an inefficient use of bus capacity and therefore is appropriate only for small communication systems using a small number of distributed processors.
Accordingly, it is desired to provide a control channel interface for a time multiplexed communication system which relieves a local processor of the burden of bus management by making the synchronous nature of the bus effectively asynchronous. The channel interface should also isolate a faulty local processor while also making more efficient use of a common bus than prior arrangements.